What is the likely cause and treatment for chronic lower back pain and stiffness, worse in the morning and improving with movement, that has persisted for months?

Axial Spondyloarthritis (Inflammatory Back Pain)

This presentation is highly suggestive of axial spondyloarthritis (axSpA), and the patient should be started on NSAIDs and referred to rheumatology for confirmation and consideration of biologic therapy if NSAIDs are insufficient. 1, 2

Clinical Diagnosis

The symptom pattern described—chronic lower back pain with morning stiffness that improves with movement and has persisted for months—represents classic inflammatory back pain, which is the hallmark presentation of axSpA and affects more than 80% of patients with this condition 1, 2, 3.

Key Diagnostic Features Present:

• Morning stiffness worse in the morning and improving with movement (not rest) is pathognomonic for inflammatory rather than mechanical back pain 1, 3
• Chronic duration (months) meets the typical criterion of ≥3 months 1
• Right-sided pain with diffuse lower back stiffness suggests sacroiliac joint involvement, which is the initial site of inflammation in axSpA 1
• The pattern of pain improving with activity but worsening with rest distinguishes this from mechanical causes like disc herniation 1, 3

Additional Features to Assess:

• Age of onset <45 years (typically 15-30 years in males) 1, 3
• Alternating buttock pain 1, 3
• Pain in the second half of the night that awakens the patient 1
• Good response to NSAIDs (a diagnostic clue) 3, 4
• Extra-articular manifestations: uveitis, psoriasis, inflammatory bowel disease 1, 2
• Family history of spondyloarthritis 3
• Peripheral joint involvement: oligoarticular asymmetric arthritis (especially knees), enthesitis, or dactylitis 1, 2

Diagnostic Workup

Laboratory Testing:

• HLA-B27 (positive in 50% of axSpA patients; specificity 90%) 2, 3
• C-reactive protein (elevated in 35% of cases; specificity 91%) 1, 2
• Note: HLA-B27 positivity increases diagnostic likelihood but is neither necessary nor sufficient for diagnosis 1, 2

Imaging Strategy:

• Start with plain radiographs of the sacroiliac joints and lumbar spine as first-line imaging 1
• MRI of sacroiliac joints is indicated if radiographs are negative but clinical suspicion remains high, as radiographic changes lag behind symptoms by 7+ years 1
• MRI can detect "preradiographic" disease through bone marrow edema on STIR or T2-weighted fat-saturated sequences 1
• MRI has 78% sensitivity and 88% specificity for sacroiliitis 2

Important Caveat:

Inform the radiologist about physically demanding activities or recent childbirth in women, as mechanical stress can mimic inflammatory findings on MRI 1

Treatment Algorithm

First-Line Therapy:

1. NSAIDs at full anti-inflammatory doses (e.g., indomethacin, naproxen) taken continuously, not as needed 1, 2, 4
2. Physical therapy and exercise to maintain mobility and function 1
3. Patient education about the chronic nature of the condition 1

Expected response: Less than 25% of patients achieve complete symptom control with NSAIDs alone 2

Second-Line Therapy (if inadequate response after 4 weeks):

Biologic DMARDs or JAK inhibitors are indicated when NSAIDs fail to control symptoms 1, 2:

• TNF inhibitors (anti-TNF agents): 58-64% achieve ASAS20 response vs. 19-38% with placebo 2
• IL-17 inhibitors: 48-61% achieve ASAS20 response vs. 18-29% with placebo 2
• JAK inhibitors: 52-56% achieve ASAS20 response vs. 26-29% with placebo 2

Critical point: Traditional DMARDs (methotrexate, sulfasalazine, leflunomide) are NOT effective for axial manifestations and should not be used for spinal disease 1

Treatment Goals:

• Target: BASDAI score <3 or reduction by 2 points, or ASDAS inactive disease (<1.3) 1
• Assessment timing: Evaluate response at 6-12 weeks 1
• Long-term goals: Prevent structural damage, maintain function, and preserve quality of life 1

Rheumatology Referral

Refer to rheumatology for:

• Confirmation of diagnosis using ASAS classification criteria 1
• Initiation of biologic therapy if NSAIDs are insufficient 1
• Monitoring for extra-articular manifestations and comorbidities 1, 2

The typical diagnostic delay is 6-8 years from symptom onset, making early recognition critical to prevent irreversible structural damage and disability 2, 3

Red Flags to Exclude

Before confirming inflammatory back pain, rule out:

• Cauda equina syndrome: urinary retention, fecal incontinence, saddle anesthesia (requires emergency evaluation) 5
• Malignancy: history of cancer, unexplained weight loss, age >50, failure to improve after 1 month 5
• Infection: fever, IV drug use, recent infection, immunocompromised status 5
• Fracture: older age, osteoporosis, steroid use 6

Common Pitfalls

• Misdiagnosing as mechanical back pain or sacroiliac joint dysfunction, delaying appropriate treatment by years 3, 4
• Ordering MRI too early without first obtaining plain radiographs 1
• Prescribing traditional DMARDs (methotrexate, sulfasalazine) for axial disease, which are ineffective 1
• Using NSAIDs "as needed" rather than continuously at anti-inflammatory doses 1, 4
• Failing to recognize that improvement with exercise (not rest) is the key distinguishing feature from mechanical causes 1, 3